Drastic reduction of dynamic liquid-solid friction in supercooled glycerol

TL;DR

This research reveals a significant decrease in liquid-solid friction in supercooled glycerol as temperature drops, linked to slowed liquid dynamics and solid surface fluctuations, challenging conventional thermally activated friction models.

Contribution

It introduces a minimalistic phonon-branch model explaining the drastic friction reduction by solid fluctuations, bridging soft and hard condensed matter physics.

Findings

Friction drops sharply with decreasing temperature in supercooled glycerol.

A phonon-branch model semi-quantitatively explains the friction behavior.

Interfacial friction is influenced by solid surface fluctuations, not just thermal activation.

Abstract

This study addresses the influence of internal liquid dynamics on liquid-solid friction. Taking advantage of the wide range of relaxation timescales in supercooled liquids, we use a tuning-fork-based AFM to measure the slippage of supercooled glycerol on mica at 30 kHz. We report a 2-order of magnitude increase of slippage with decreasing temperature by only 30{\deg}C. More importantly, as the bulk liquid dynamics are slowed with decreasing temperature, we report a sharp drop of the interfacial friction coefficient in contrast with the usual assumption of thermally activated interfacial dynamics. To rationalize this original behavior, we account for the contribution of solid fluctuations to liquid friction. We show that a minimalistic single phonon-branch model of the mica surface yields semi-quantitative agreement with our measurements. In this picture, the liquid's relaxation rate is the tuning knob between two friction regimes where the wall is seen either as a static corrugated potential or as a thermally fluctuating surface. Remarkably, this study bridges soft and hard condensed matter: hydrodynamic flow controlled by the solid's dynamical modes.